1. Field of the Invention
The present invention relates to processing of data in a communications system. In particular the present invention relates to processing of data received from a communications device over a wireless interface.
2. Description of the Related Art
A communication system can be seen as a facility that enables communication sessions between two or more entities such as user equipment and/or other nodes associated with the communication system. The communication may comprise, for example, communication of voice, data, multimedia and so on. Communication systems providing wireless communication for user equipment are known. Cellular communication systems are configured to have a cell structure, and typically they support communication with user equipment changing locations (mobile users). The support for communications for mobile users may include support for handing existing connections from one cell to another cell. At least routing of calls or communications for a mobile user in a new cell is typically supported in cellular systems. Some examples of a cellular system are the Global System for Mobile Telecommunications (GSM) and General Packet Radio Service (GPRS). GPRS provides packet-switched data services and utilizes the infrastructure of a GSM system. Further examples of a cellular system are third generation telecommunication systems, which typically support both packet-switched and circuit-switched data transfer. The Wideband Code Division Multiple Access (WCDMA) system is one example of a third generation cellular telecommunication system.
For illustrating packet-switched services in cellular system, the WCDMA system is used below as an example. It is, however, appreciated, that similar concepts may be found also in other cellular systems supporting packet-switched services.
FIG. 1 illustrates schematically, as an example of a cellular network supporting packet-switched services, a WCDMA network 100. Only some of the network elements of a WCDMA network are illustrated in FIG. 1. The radio access network 110 comprises a number of a radio network controllers (RNC) 116 and a number of base transceiver stations (BS) 114. Base stations are often called Node B's in connection with the WCDMA. A communications device 101, typically called a mobile station (MS) or user equipment (UE), communicates with a base transceiver station 114 over a radio interface. The packet-switched core network 120 of the system 100 comprises a number of GPRS Supporting Nodes (GSN) 122. Each mobile station registered for packet-switched services has a serving GSN, called SGSN, which is responsible for controlling the packet-switched connections to and from the mobile station. The packet-switched core network 120 is typically connected to further packet-switched networks via a Gateway GSN 124 (GGSN).
FIG. 2 shows, as an example of user plane protocol stacks, a protocol stack 201 for a communications device 101, a protocol stack 214 for the transceiver station 114, and protocol stacks 216a, 216b for a drift radio network controller and for a serving radio network controller. FIG. 2 also shows a protocol stack 222 for a serving GSN 122 and a protocol stack 224 for the GGSN 124. Even without a detailed discussion of the protocols mentioned in FIG. 2, it is possible to see that the protocol stacks reflect the hierarchical structure of a cellular communication system. Consider, as an example, the protocol stack 201 of the communications device 101 and the network element where the other endpoint of a logical protocol connection is. For the lowest protocol layer (physical layer PHY) in the protocol stack 201 the other endpoint is the base transceiver station 114. This is also true for part of medium access control (MAC) layer in the protocol stack 201 (see discussion below in connection with High-speed packet access). For higher protocol layers (part of physical layer, MAC layer, Radio Link Control (RLC) and L3 layer) in the protocol stack 201, the other endpoint is the serving RNC. For the Internet Protocol (IP) layer, the other endpoint is the GGSN.
In WCDMA the access technique is based on code division and same frequency ranges can be used by neighboring base transceiver stations. In principle, data transfer may occur between a communications device and one or more than one base transceiver stations. The base transceiver station(s) with which a communications device is communicating typically depends on the radio link quality between the communications device and the base transceiver stations nearby. When signals sent by a communications device are processed by a number of base transceiver stations, diversity combining of the received signals may be used to increase data transmission quality and throughput. Similarly, in the downlink direction transmission diversity schemes may be used.
Packet data transmission is supported by dedicated channels (DCHs), by shared channels (more specifically by a Downlink-shared Channel DSCH) and by a Forward Access channel, which is carried on a common control physical channel, already in the early releases of WCDMA specifications. To increase downlink packet data transfer capacity, a concept called High-speed Downlink Packet Access (HSDPA) has been designed by the Third Generation Partnership Project (3GPP) for the WCDMA system. HSDPA is discussed, for example, in Chapter 11 in WCDMA for UMTS, Third edition, Eds. Harri Holma and Antti Toskala, Wiley and Sons, 2004.
In HSDPA the packet data throughput is increased by using techniques such as link adaptation and fast physical layer (L1) retransmission combining. The logical channel for downlink user data is called High-speed Downlink Shared Channel (HS-DSCH) in HSDPA. For sending acknowledgment information (AKC/NACK) relating to L1 retransmission and quality feedback information, there is defined a specific uplink control channel. The endpoint of this uplink control channel are a communications device and a base transceiver station (not a radio network controller).
In HSDPA, diversity combining is not used in the downlink direction in connection with the HS-DSCH. This is because the advanced link level techniques in HS-DSCH can tolerate fading and the macro diversity combining is not necessary. HSDPA also supports cell change where the HS-DSCH transmission is changed from one cell to another. That process takes typically a few hundreds of milliseconds. The control channel DPCCH associated with the shared data channel HS-DCSH uses soft handover (diversity combining).
For supporting an increased packet data transfer capacity also in the uplink direction, an uplink shared channel for packet data may also be defined. A concept called High-speed Uplink Packet Access (HSUPA) has been standardized as part of 3GPP Release 6. The work item was called Enhanced uplink DCH. In the uplink direction there is typically need for diversity combining for ensuring a sufficiently high quality and reliability of data transfer and for controlling interference. Diversity combinining is also needed for ensuring reliable data transfer for handover situations (soft handovers). In the proposed HSUPA concept, two base transceiver stations process the signals received from a communications device and the processed information is then combined in a serving radio network controller.
In addition to cellular communications system having a similar hierarchy than the hierarchy of base transceiver stations, radio network controllers and GPRS support nodes, wireless communications are provided by non-cellular communication systems. One solution is to connect transceiver network elements directly to a packet-switched network and use protocols similar to those in fixed packet-switched networks also for providing the wireless packet data access. One example of these non-cellular wireless networks is the Wireless Local Area Network (WLAN). basic mobility support may be provided, for example, based on the Mobile IP protocol. Cellular communication systems, however, are typically able to support mobility in a more enhanced manner than non-cellular wireless communication systems. Cellular communications systems, for example, support continuous connections to a mobile communications device. Changing the access point from one transceiver network element to another typically causes an interruption to a connection in non-cellular communication systems. A further advantage of cellular communication systems is that they typically have versatile authentication, accounting and authorization schemes implemented therein.
A network architecture with less hierarchy levels is often more easily scalable than a network architecture with more hierarchy levels. The various protocols and network elements in a hierarchical network architecture may in some cases cause delays, which degrade an end-user experience. Simplification of the hierarchical communication system, especially in connection with packet data transfer, may thus provide some advantages.
On the other hand, certain functionality and interfaces between network elements and between a communications device and the cellular communications system are typically defined in the relevant specifications for the cellular communications systems. Therefore the standardized functionality and features have to be taken into account when envisaging changes to the cellular network architecture.
Considering the high-speed packet access in the uplink direction, there are open questions relating to how to support a change from one base transceiver station to another in connection with a distributed (non-hierarchical) network architecture and how to support diversity combining. As mentioned above, the current 3GPP specifications define a soft handover, where two base transceiver stations receive and process signals sent by a communications device and the processed signals are diversity combined in a radio network controller. Should the network be implemented differently than shown in FIG. 1, the communications device should not need modifications.
It is appreciated that although above reference is made mainly to the HSDPA/HSUPA and to the WCDMA system, the problems may be relevant also for other communication systems.